1. Field of the Invention
The present invention relates to an image processing system, image processing method, and an image processing program product capable of reducing the noise caused by the image pickup system.
2. Description of the Related Art
In general, a digital image pickup unit, for example, digital camera, digital video camera and the like includes an image pickup device, an analog circuit for subjecting the analog signal outputted from the image pickup device to various analog processings, and an A/D converter for converting the signal from the analog circuit into a digital signal.
The digital signal derived from the A/D converter of the digital image pickup unit generally contains noise which may be mainly classified into two types, that is, random noise and spike noise.
The random noise is generated in the image pickup device and the analog circuit, and has the characteristics similar to white noise properties.
Meanwhile, the spike noise is mainly caused by the image pickup device, and is typified by defective pixels or the like.
Various proposals for reducing the noise have been introduced.
Japanese Unexamined Patent Application Publication No. 2004-72422 discloses that the generation amount of the random noise for each color signal is subjected to modeling to dynamically estimate the noise amount such that the noise reducing process is performed. The disclosed technology allows the highly accurate noise reducing process for each pixel under no influence of the shooting condition.
Japanese Unexamined Patent Application Publication No. 6-205216 discloses that the determination is made as to whether or not the spike noise, and upon detection of the spike noise, the median filtering process is performed while enlarging the size of the block to be processed. This makes it possible to allow the stable noise reducing process with respect to various types of the spike noise.
Japanese Unexamined Patent Application Publication No. 8-36640 discloses the technology with respect to general noise, more specifically, the technology for vectorizing RGB signal to correct the vector signal so as to minimize the evaluation function inside the vector space. This makes it possible to reduce the color noise while maintaining the edge regions.
According to the technology disclosed in Japanese Unexamined Patent Application Publication No. 2004-72422, the random noise may be sufficiently reduced, but the spike noise cannot be sufficiently reduced. The technology is intended to perform the noise reducing process for each color signal, which requires the processing a plurality of times corresponding to the number of the color signals. This may elongate the processing time.
According to the technology disclosed in Japanese Unexamined Patent Application Publication No. 6-205216, the median filtering process is performed while enlarging the block size sequentially. This may sufficiently reduce the spike noise. However, the limit to which the block size is allowed to be enlarged becomes different depending on the subject to be processed, resulting in the unstable and long processing time. Additionally, as the median filtering process is independently performed for each color signal, some pixel may have the hue sharply changed.
According to the technology disclosed in Japanese Unexamined Patent Application Publication No. 8-36640, the appropriate setting of the evaluation function allows the general noise to be reduced in good condition. However, it is difficult to automatically set the appropriate evaluation function. In the technology, the processing is required to be performed recurrently until the evaluation function converges, resulting in unstable and elongated processing time.
It is an object of the present invention to provide an image processing system, image processing method, and an image processing program product capable of automatically performing the highly accurate noise reducing process.
It is another object of the present invention to provide an image processing system, image processing method, and an image processing program product capable of performing the high speed noise reducing process without causing the adverse effect such as change in the hue.